C++ DR1611, 1658, 2180: implement "potentially constructed subobject" rules for special member functions.

Essentially, as a base class constructor does not construct virtual bases, such
a constructor for an abstract class does not need the corresponding base class
construction to be valid, and likewise for destructors.

This creates an awkward situation: clang will sometimes generate references to
the complete object and deleting destructors for an abstract class (it puts
them in the construction vtable for a derived class). But we can't generate a
"correct" version of these because we can't generate references to base class
constructors any more (if they're template specializations, say, we might not
have instantiated them and can't assume any other TU will emit a copy).
Fortunately, we don't need to, since no correct program can ever invoke them,
so instead emit symbols that just trap.

We should stop emitting references to these symbols, but still need to emit
definitions for compatibility.

llvm-svn: 296275

clang/include/clang/AST/DeclCXX.h

@@ -441,9 +441,10 @@ class CXXRecordDecl : public RecordDecl {
     /// either by the user or implicitly.
     unsigned DeclaredSpecialMembers : 6;
 
-    /// \brief Whether an implicit copy constructor would have a const-qualified
-    /// parameter.
-    unsigned ImplicitCopyConstructorHasConstParam : 1;
+    /// \brief Whether an implicit copy constructor could have a const-qualified
+    /// parameter, for initializing virtual bases and for other subobjects.
+    unsigned ImplicitCopyConstructorCanHaveConstParamForVBase : 1;
+    unsigned ImplicitCopyConstructorCanHaveConstParamForNonVBase : 1;
 
     /// \brief Whether an implicit copy assignment operator would have a
     /// const-qualified parameter.
@@ -882,7 +883,9 @@ public:
   /// \brief Determine whether an implicit copy constructor for this type
   /// would have a parameter with a const-qualified reference type.
   bool implicitCopyConstructorHasConstParam() const {
-    return data().ImplicitCopyConstructorHasConstParam;
+    return data().ImplicitCopyConstructorCanHaveConstParamForNonVBase &&
+           (isAbstract() ||
+            data().ImplicitCopyConstructorCanHaveConstParamForVBase);
   }
 
   /// \brief Determine whether this class has a copy constructor with

clang/lib/AST/ASTImporter.cpp

@@ -2363,8 +2363,10 @@ bool ASTNodeImporter::ImportDefinition(RecordDecl *From, RecordDecl *To,
     ToData.UserProvidedDefaultConstructor
       = FromData.UserProvidedDefaultConstructor;
     ToData.DeclaredSpecialMembers = FromData.DeclaredSpecialMembers;
-    ToData.ImplicitCopyConstructorHasConstParam
-      = FromData.ImplicitCopyConstructorHasConstParam;
+    ToData.ImplicitCopyConstructorCanHaveConstParamForVBase
+      = FromData.ImplicitCopyConstructorCanHaveConstParamForVBase;
+    ToData.ImplicitCopyConstructorCanHaveConstParamForNonVBase
+      = FromData.ImplicitCopyConstructorCanHaveConstParamForNonVBase;
     ToData.ImplicitCopyAssignmentHasConstParam
       = FromData.ImplicitCopyAssignmentHasConstParam;
     ToData.HasDeclaredCopyConstructorWithConstParam

clang/lib/AST/DeclCXX.cpp

@@ -68,7 +68,8 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       HasConstexprDefaultConstructor(false),
       HasNonLiteralTypeFieldsOrBases(false), ComputedVisibleConversions(false),
       UserProvidedDefaultConstructor(false), DeclaredSpecialMembers(0),
-      ImplicitCopyConstructorHasConstParam(true),
+      ImplicitCopyConstructorCanHaveConstParamForVBase(true),
+      ImplicitCopyConstructorCanHaveConstParamForNonVBase(true),
       ImplicitCopyAssignmentHasConstParam(true),
       HasDeclaredCopyConstructorWithConstParam(false),
       HasDeclaredCopyAssignmentWithConstParam(false), IsLambda(false),
@@ -227,7 +228,7 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
         //   'const B&' or 'const volatile B&' [...]
         if (CXXRecordDecl *VBaseDecl = VBase.getType()->getAsCXXRecordDecl())
           if (!VBaseDecl->hasCopyConstructorWithConstParam())
-            data().ImplicitCopyConstructorHasConstParam = false;
+            data().ImplicitCopyConstructorCanHaveConstParamForVBase = false;
 
         // C++1z [dcl.init.agg]p1:
         //   An aggregate is a class with [...] no virtual base classes
@@ -264,6 +265,14 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
       //   In the definition of a constexpr constructor [...]
       //    -- the class shall not have any virtual base classes
       data().DefaultedDefaultConstructorIsConstexpr = false;
+
+      // C++1z [class.copy]p8:
+      //   The implicitly-declared copy constructor for a class X will have
+      //   the form 'X::X(const X&)' if each potentially constructed subobject
+      //   has a copy constructor whose first parameter is of type
+      //   'const B&' or 'const volatile B&' [...]
+      if (!BaseClassDecl->hasCopyConstructorWithConstParam())
+        data().ImplicitCopyConstructorCanHaveConstParamForVBase = false;
     } else {
       // C++ [class.ctor]p5:
       //   A default constructor is trivial [...] if:
@@ -306,6 +315,14 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
       //   default constructor is constexpr.
       if (!BaseClassDecl->hasConstexprDefaultConstructor())
         data().DefaultedDefaultConstructorIsConstexpr = false;
+
+      // C++1z [class.copy]p8:
+      //   The implicitly-declared copy constructor for a class X will have
+      //   the form 'X::X(const X&)' if each potentially constructed subobject
+      //   has a copy constructor whose first parameter is of type
+      //   'const B&' or 'const volatile B&' [...]
+      if (!BaseClassDecl->hasCopyConstructorWithConstParam())
+        data().ImplicitCopyConstructorCanHaveConstParamForNonVBase = false;
     }
 
     // C++ [class.ctor]p3:
@@ -325,14 +342,6 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
     if (!BaseClassDecl->hasCopyAssignmentWithConstParam())
       data().ImplicitCopyAssignmentHasConstParam = false;
 
-    // C++11 [class.copy]p8:
-    //   The implicitly-declared copy constructor for a class X will have
-    //   the form 'X::X(const X&)' if each direct [...] base class B of X
-    //   has a copy constructor whose first parameter is of type
-    //   'const B&' or 'const volatile B&' [...]
-    if (!BaseClassDecl->hasCopyConstructorWithConstParam())
-      data().ImplicitCopyConstructorHasConstParam = false;
-
     // A class has an Objective-C object member if... or any of its bases
     // has an Objective-C object member.
     if (BaseClassDecl->hasObjectMember())
@@ -916,12 +925,11 @@ void CXXRecordDecl::addedMember(Decl *D) {
 
         // C++11 [class.copy]p8:
         //   The implicitly-declared copy constructor for a class X will have
-        //   the form 'X::X(const X&)' if [...] for all the non-static data
-        //   members of X that are of a class type M (or array thereof), each
-        //   such class type has a copy constructor whose first parameter is
-        //   of type 'const M&' or 'const volatile M&'.
+        //   the form 'X::X(const X&)' if each potentially constructed subobject
+        //   of a class type M (or array thereof) has a copy constructor whose
+        //   first parameter is of type 'const M&' or 'const volatile M&'.
         if (!FieldRec->hasCopyConstructorWithConstParam())
-          data().ImplicitCopyConstructorHasConstParam = false;
+          data().ImplicitCopyConstructorCanHaveConstParamForNonVBase = false;
 
         // C++11 [class.copy]p18:
         //   The implicitly-declared copy assignment oeprator for a class X will

clang/lib/CodeGen/CGClass.cpp

@@ -1390,6 +1390,20 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
   const CXXDestructorDecl *Dtor = cast<CXXDestructorDecl>(CurGD.getDecl());
   CXXDtorType DtorType = CurGD.getDtorType();
 
+  // For an abstract class, non-base destructors are never used (and can't
+  // be emitted in general, because vbase dtors may not have been validated
+  // by Sema), but the Itanium ABI doesn't make them optional and Clang may
+  // in fact emit references to them from other compilations, so emit them
+  // as functions containing a trap instruction.
+  if (DtorType != Dtor_Base && Dtor->getParent()->isAbstract()) {
+    llvm::CallInst *TrapCall = EmitTrapCall(llvm::Intrinsic::trap);
+    TrapCall->setDoesNotReturn();
+    TrapCall->setDoesNotThrow();
+    Builder.CreateUnreachable();
+    Builder.ClearInsertionPoint();
+    return;
+  }
+
   Stmt *Body = Dtor->getBody();
   if (Body)
     incrementProfileCounter(Body);

clang/lib/Sema/SemaDeclCXX.cpp

@@ -5081,6 +5081,10 @@ Sema::MarkBaseAndMemberDestructorsReferenced(SourceLocation Location,
     DiagnoseUseOfDecl(Dtor, Location);
   }
 
+  // We only potentially invoke the destructors of potentially constructed
+  // subobjects.
+  bool VisitVirtualBases = !ClassDecl->isAbstract();
+
   llvm::SmallPtrSet<const RecordType *, 8> DirectVirtualBases;
 
   // Bases.
@@ -5089,8 +5093,11 @@ Sema::MarkBaseAndMemberDestructorsReferenced(SourceLocation Location,
     const RecordType *RT = Base.getType()->getAs<RecordType>();
 
     // Remember direct virtual bases.
-    if (Base.isVirtual())
+    if (Base.isVirtual()) {
+      if (!VisitVirtualBases)
+        continue;
       DirectVirtualBases.insert(RT);
+    }
 
     CXXRecordDecl *BaseClassDecl = cast<CXXRecordDecl>(RT->getDecl());
     // If our base class is invalid, we probably can't get its dtor anyway.
@@ -5112,6 +5119,9 @@ Sema::MarkBaseAndMemberDestructorsReferenced(SourceLocation Location,
     MarkFunctionReferenced(Location, Dtor);
     DiagnoseUseOfDecl(Dtor, Location);
   }
+
+  if (!VisitVirtualBases)
+    return;
   
   // Virtual bases.
   for (const auto &VBase : ClassDecl->vbases()) {
@@ -6881,11 +6891,13 @@ bool Sema::ShouldDeleteSpecialMember(CXXMethodDecl *MD, CXXSpecialMember CSM,
   SpecialMemberDeletionInfo SMI(*this, MD, CSM, ICI, Diagnose);
 
   // Per DR1611, do not consider virtual bases of constructors of abstract
-  // classes, since we are not going to construct them. For assignment
-  // operators, we only assign (and thus only consider) direct bases.
-  if (SMI.visit(SMI.IsConstructor ? SMI.VisitPotentiallyConstructedBases :
-                SMI.IsAssignment  ? SMI.VisitDirectBases :
-                                    SMI.VisitAllBases))
+  // classes, since we are not going to construct them.
+  // Per DR1658, do not consider virtual bases of destructors of abstract
+  // classes either.
+  // Per DR2180, for assignment operators we only assign (and thus only
+  // consider) direct bases.
+  if (SMI.visit(SMI.IsAssignment ? SMI.VisitDirectBases
+                                 : SMI.VisitPotentiallyConstructedBases))
     return true;
 
   if (SMI.shouldDeleteForAllConstMembers())
@@ -10192,15 +10204,15 @@ ComputeDefaultedSpecialMemberExceptionSpec(
   //   destructor without a noexcept-specifier, is potentially-throwing if and
   //   only if any of the destructors for any of its potentially constructed
   //   subojects is potentially throwing.
-  // FIXME: We should respect the first rule but ignore the "potentially
-  // constructed" in the second rule to resolve a core issue (no number yet)
-  // that would have us reject:
+  // FIXME: We respect the first rule but ignore the "potentially constructed"
+  // in the second rule to resolve a core issue (no number yet) that would have
+  // us reject:
   //   struct A { virtual void f() = 0; virtual ~A() noexcept(false) = 0; };
   //   struct B : A {};
   //   struct C : B { void f(); };
   // ... due to giving B::~B() a non-throwing exception specification.
-  // For now we don't implement either.
-  Info.visit(Info.VisitAllBases);
+  Info.visit(Info.IsConstructor ? Info.VisitPotentiallyConstructedBases
+                                : Info.VisitAllBases);
 
   return Info.ExceptSpec;
 }

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -1524,7 +1524,8 @@ void ASTDeclReader::ReadCXXDefinitionData(
   Data.ComputedVisibleConversions = Record.readInt();
   Data.UserProvidedDefaultConstructor = Record.readInt();
   Data.DeclaredSpecialMembers = Record.readInt();
-  Data.ImplicitCopyConstructorHasConstParam = Record.readInt();
+  Data.ImplicitCopyConstructorCanHaveConstParamForVBase = Record.readInt();
+  Data.ImplicitCopyConstructorCanHaveConstParamForNonVBase = Record.readInt();
   Data.ImplicitCopyAssignmentHasConstParam = Record.readInt();
   Data.HasDeclaredCopyConstructorWithConstParam = Record.readInt();
   Data.HasDeclaredCopyAssignmentWithConstParam = Record.readInt();
@@ -1654,7 +1655,8 @@ void ASTDeclReader::MergeDefinitionData(
   // ComputedVisibleConversions is handled below.
   MATCH_FIELD(UserProvidedDefaultConstructor)
   OR_FIELD(DeclaredSpecialMembers)
-  MATCH_FIELD(ImplicitCopyConstructorHasConstParam)
+  MATCH_FIELD(ImplicitCopyConstructorCanHaveConstParamForVBase)
+  MATCH_FIELD(ImplicitCopyConstructorCanHaveConstParamForNonVBase)
   MATCH_FIELD(ImplicitCopyAssignmentHasConstParam)
   OR_FIELD(HasDeclaredCopyConstructorWithConstParam)
   OR_FIELD(HasDeclaredCopyAssignmentWithConstParam)

clang/lib/Serialization/ASTWriter.cpp

@@ -5703,7 +5703,8 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
   Record->push_back(Data.ComputedVisibleConversions);
   Record->push_back(Data.UserProvidedDefaultConstructor);
   Record->push_back(Data.DeclaredSpecialMembers);
-  Record->push_back(Data.ImplicitCopyConstructorHasConstParam);
+  Record->push_back(Data.ImplicitCopyConstructorCanHaveConstParamForVBase);
+  Record->push_back(Data.ImplicitCopyConstructorCanHaveConstParamForNonVBase);
   Record->push_back(Data.ImplicitCopyAssignmentHasConstParam);
   Record->push_back(Data.HasDeclaredCopyConstructorWithConstParam);
   Record->push_back(Data.HasDeclaredCopyAssignmentWithConstParam);

clang/test/CXX/drs/dr16xx.cpp

@@ -3,6 +3,13 @@
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++1z -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 
+namespace dr1611 { // dr1611: dup 1658
+  struct A { A(int); };
+  struct B : virtual A { virtual void f() = 0; };
+  struct C : B { C() : A(0) {} void f(); };
+  C c;
+}
+
 namespace dr1684 { // dr1684: 3.6
 #if __cplusplus >= 201103L
   struct NonLiteral { // expected-note {{because}}
@@ -101,3 +108,114 @@ namespace dr1653 { // dr1653: 4 c++17
     b -= 1; // ok
   }
 }
+
+namespace dr1658 { // dr1658: 5
+  namespace DefCtor {
+    class A { A(); }; // expected-note 0-2{{here}}
+    class B { ~B(); }; // expected-note 0-2{{here}}
+
+    // The stars align! An abstract class does not construct its virtual bases.
+    struct C : virtual A { C(); virtual void foo() = 0; };
+    C::C() = default; // ok, not deleted, expected-error 0-1{{extension}}
+    struct D : virtual B { D(); virtual void foo() = 0; };
+    D::D() = default; // ok, not deleted, expected-error 0-1{{extension}}
+
+    // In all other cases, we are not so lucky.
+    struct E : A { E(); virtual void foo() = 0; };
+#if __cplusplus < 201103L
+    E::E() = default; // expected-error {{private default constructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    E::E() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible default constructor}}
+#endif
+    struct F : virtual A { F(); };
+#if __cplusplus < 201103L
+    F::F() = default; // expected-error {{private default constructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    F::F() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible default constructor}}
+#endif
+
+    struct G : B { G(); virtual void foo() = 0; };
+#if __cplusplus < 201103L
+    G::G() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    G::G() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+    struct H : virtual B { H(); };
+#if __cplusplus < 201103L
+    H::H() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    H::H() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+  }
+
+  namespace Dtor {
+    class B { ~B(); }; // expected-note 0-2{{here}}
+
+    struct D : virtual B { ~D(); virtual void foo() = 0; };
+    D::~D() = default; // ok, not deleted, expected-error 0-1{{extension}}
+
+    struct G : B { ~G(); virtual void foo() = 0; };
+#if __cplusplus < 201103L
+    G::~G() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    G::~G() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+    struct H : virtual B { ~H(); };
+#if __cplusplus < 201103L
+    H::~H() = default; // expected-error@-2 {{private destructor}} expected-error {{extension}} expected-note {{here}}
+#else
+    H::~H() = default; // expected-error {{would delete}} expected-note@-4{{inaccessible destructor}}
+#endif
+  }
+
+  namespace MemInit {
+    struct A { A(int); }; // expected-note {{here}}
+    struct B : virtual A {
+      B() {}
+      virtual void f() = 0;
+    };
+    struct C : virtual A {
+      C() {} // expected-error {{must explicitly initialize}}
+    };
+  }
+
+  namespace CopyCtorParamType {
+    struct A { A(A&); };
+    struct B : virtual A { virtual void f() = 0; };
+    struct C : virtual A { virtual void f(); };
+    struct D : A { virtual void f() = 0; };
+
+    struct X {
+      friend B::B(const B&) throw();
+      friend C::C(C&);
+      friend D::D(D&);
+    };
+  }
+
+  namespace CopyCtor {
+    class A { A(const A&); A(A&&); }; // expected-note 0-4{{here}} expected-error 0-1{{extension}}
+
+    struct C : virtual A { C(const C&); C(C&&); virtual void foo() = 0; }; // expected-error 0-1{{extension}}
+    C::C(const C&) = default; // expected-error 0-1{{extension}}
+    C::C(C&&) = default; // expected-error 0-2{{extension}}
+
+    struct E : A { E(const E&); E(E&&); virtual void foo() = 0; }; // expected-error 0-1{{extension}}
+#if __cplusplus < 201103L
+    E::E(const E&) = default; // expected-error {{private copy constructor}} expected-error {{extension}} expected-note {{here}}
+    E::E(E&&) = default; // expected-error {{private move constructor}} expected-error 2{{extension}} expected-note {{here}}
+#else
+    E::E(const E&) = default; // expected-error {{would delete}} expected-note@-5{{inaccessible copy constructor}}
+    E::E(E&&) = default; // expected-error {{would delete}} expected-note@-6{{inaccessible move constructor}}
+#endif
+    struct F : virtual A { F(const F&); F(F&&); }; // expected-error 0-1{{extension}}
+#if __cplusplus < 201103L
+    F::F(const F&) = default; // expected-error {{private copy constructor}} expected-error {{extension}} expected-note {{here}}
+    F::F(F&&) = default; // expected-error {{private move constructor}} expected-error 2{{extension}} expected-note {{here}}
+#else
+    F::F(const F&) = default; // expected-error {{would delete}} expected-note@-5{{inaccessible copy constructor}}
+    F::F(F&&) = default; // expected-error {{would delete}} expected-note@-6{{inaccessible move constructor}}
+#endif
+  }
+
+  // assignment case is superseded by dr2180
+}

clang/test/CXX/drs/dr21xx.cpp

@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -std=c++98 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++1z -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+
+namespace dr2180 { // dr2180: yes
+  class A {
+    A &operator=(const A &); // expected-note 0-2{{here}}
+    A &operator=(A &&); // expected-note 0-2{{here}} expected-error 0-1{{extension}}
+  };
+
+  struct B : virtual A {
+    B &operator=(const B &);
+    B &operator=(B &&); // expected-error 0-1{{extension}}
+    virtual void foo() = 0;
+  };
+#if __cplusplus < 201103L
+  B &B::operator=(const B&) = default; // expected-error {{private member}} expected-error {{extension}} expected-note {{here}}
+  B &B::operator=(B&&) = default; // expected-error {{private member}} expected-error 2{{extension}} expected-note {{here}}
+#else
+  B &B::operator=(const B&) = default; // expected-error {{would delete}} expected-note@-9{{inaccessible copy assignment}}
+  B &B::operator=(B&&) = default; // expected-error {{would delete}} expected-note@-10{{inaccessible move assignment}}
+#endif
+}

clang/test/CodeGenCXX/constructors.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 %s -emit-llvm -o - | FileCheck %s --implicit-check-not=should_not_appear_in_output
 
 struct Member { int x; Member(); Member(int); Member(const Member &); };
 struct VBase { int x; VBase(); VBase(int); VBase(const VBase &); };
@@ -109,3 +109,57 @@ namespace test1 {
   // CHECK:      [[THIS:%.*]] = load [[B:%.*]]*, [[B:%.*]]**
   // CHECK-NEXT: ret void
 }
+
+// Ensure that we
+// a) emit the ABI-required but useless complete object and deleting destructor
+//    symbols for an abstract class, and 
+// b) do *not* emit references to virtual base destructors for an abstract class
+//
+// Our approach to this is to give these functions a body that simply traps.
+//
+// FIXME: We should ideally not create these symbols at all, but Clang can
+// actually generate references to them in other TUs in some cases, so we can't
+// stop emitting them without breaking ABI. See:
+//
+//   https://github.com/itanium-cxx-abi/cxx-abi/issues/10
+namespace abstract {
+  // Note, the destructor of this class is not instantiated here.
+  template<typename T> struct should_not_appear_in_output {
+    ~should_not_appear_in_output() { int arr[-(int)sizeof(T)]; }
+  };
+
+  struct X { ~X(); };
+
+  struct A : virtual should_not_appear_in_output<int>, X {
+    virtual ~A() = 0;
+  };
+
+  // CHECK-LABEL: define void @_ZN8abstract1AD2Ev(
+  // CHECK: call {{.*}}@_ZN8abstract1XD2Ev(
+  // CHECK: ret
+
+  // CHECK-LABEL: define void @_ZN8abstract1AD1Ev(
+  // CHECK: call {{.*}}@llvm.trap(
+  // CHECK: unreachable
+
+  // CHECK-LABEL: define void @_ZN8abstract1AD0Ev(
+  // CHECK: call {{.*}}@llvm.trap(
+  // CHECK: unreachable
+  A::~A() {}
+
+  struct B : virtual should_not_appear_in_output<int>, X {
+    virtual void f() = 0;
+    ~B();
+  };
+
+  // CHECK-LABEL: define void @_ZN8abstract1BD2Ev(
+  // CHECK: call {{.*}}@_ZN8abstract1XD2Ev(
+  // CHECK: ret
+
+  // CHECK-LABEL: define void @_ZN8abstract1BD1Ev(
+  // CHECK: call {{.*}}@llvm.trap(
+  // CHECK: unreachable
+
+  // CHECK-NOT: @_ZN8abstract1BD0Ev(
+  B::~B() {}
+}

clang/test/CodeGenCXX/implicit-exception-spec.cpp

@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 %s -triple=x86_64-linux-gnu -emit-llvm -std=c++11 -o - -fcxx-exceptions -fexceptions | FileCheck -check-prefix=CHECK %s
+
+struct A {
+  A();
+  A(const A&);
+  A(A&&);
+};
+struct B : virtual A {
+  virtual void f() = 0;
+};
+struct C : B {
+  void f();
+};
+
+// CHECK-DAG: define {{.*}} @_ZN1BC2Ev({{.*}} #[[NOUNWIND:[0-9]*]]
+C c1;
+// CHECK-DAG: define {{.*}} @_ZN1BC2ERKS_({{.*}} #[[NOUNWIND]]
+C c2(c1);
+// CHECK-DAG: define {{.*}} @_ZN1BC2EOS_({{.*}} #[[NOUNWIND]]
+C c3(static_cast<C&&>(c1));
+
+// CHECK-DAG: #[[NOUNWIND]] = {{{.*}} nounwind

clang/test/SemaCXX/implicit-exception-spec.cpp

@@ -92,3 +92,61 @@ namespace ImplicitDtorExceptionSpec {
     } e;
   };
 }
+
+struct nothrow_t {} nothrow;
+void *operator new(decltype(sizeof(0)), nothrow_t) noexcept;
+
+namespace PotentiallyConstructed {
+  template<bool NE> struct A {
+    A() noexcept(NE);
+    A(const A&) noexcept(NE);
+    A(A&&) noexcept(NE);
+    A &operator=(const A&) noexcept(NE);
+    A &operator=(A&&) noexcept(NE);
+    ~A() noexcept(NE);
+  };
+
+  template<bool NE> struct B : virtual A<NE> {};
+
+  template<bool NE> struct C : virtual A<NE> {
+    virtual void f() = 0; // expected-note 2{{unimplemented}}
+  };
+
+  template<bool NE> struct D final : C<NE> {
+    void f();
+  };
+
+  template<typename T, bool A, bool B, bool C, bool D, bool E, bool F> void check() {
+    T *p = nullptr;
+    T &a = *p;
+    static_assert(noexcept(a = a) == D, "");
+    static_assert(noexcept(a = static_cast<T&&>(a)) == E, "");
+    static_assert(noexcept(delete &a) == F, ""); // expected-warning 2{{abstract}}
+
+    // These are last because the first failure here causes instantiation to bail out.
+    static_assert(noexcept(new (nothrow) T()) == A, ""); // expected-error 2{{abstract}}
+    static_assert(noexcept(new (nothrow) T(a)) == B, "");
+    static_assert(noexcept(new (nothrow) T(static_cast<T&&>(a))) == C, "");
+  }
+
+  template void check<A<false>, 0, 0, 0, 0, 0, 0>();
+  template void check<A<true >, 1, 1, 1, 1, 1, 1>();
+  template void check<B<false>, 0, 0, 0, 0, 0, 0>();
+  template void check<B<true >, 1, 1, 1, 1, 1, 1>();
+  template void check<C<false>, 1, 1, 1, 0, 0, 0>(); // expected-note {{instantiation}}
+  template void check<C<true >, 1, 1, 1, 1, 1, 1>(); // expected-note {{instantiation}}
+  template void check<D<false>, 0, 0, 0, 0, 0, 0>();
+  template void check<D<true >, 1, 1, 1, 1, 1, 1>();
+
+  // ... the above trick doesn't work for this case...
+  struct Cfalse : virtual A<false> {
+    virtual void f() = 0;
+
+    Cfalse() noexcept;
+    Cfalse(const Cfalse&) noexcept;
+    Cfalse(Cfalse&&) noexcept;
+  };
+  Cfalse::Cfalse() noexcept = default;
+  Cfalse::Cfalse(const Cfalse&) noexcept = default;
+  Cfalse::Cfalse(Cfalse&&) noexcept = default;
+}